This research will investigate the physiological and anatomical differences between bipolar cells in the vertebrate retina, which carry visual signals from photoreceptors in the outer retina to amacrine and ganglion cells in the inner retina. Their interactions with each other and with other neurons form the basis of the receptive field, the building block of visual perception. It is uncertain, however, why there are multiple types of bipolar cells. I will test the hypothesis that bipolar cells whose light responses have similar thresholds and spectral sensitivities to cones receive synapses exclusively from cones and have axons that ramify close to the middle of the inner plexiform layer (IPL), and bipolar cells with light responses reflecting mixed rod/cone input receive synapses from both rods and cones and have axons that ramify near the edges of the IPL. Some bipolar cells have light responses that reverse at very positive apparent reversal potentials, and my hypothesis is that these bipolar cells are strongly electrically- coupled with other bipolar cells via gap junctions. I will test this hypothesis by recording light-evoked responses from bipolar cells in the presence and absence of agents that close gap junctions, and then analyze the axons of recorded and filled cells in the electron microscope for the presence of gap junctions.